While climate change adversely affects many bird species, migratory bird species may suffer the greatest challenges, largely because their migration patterns take them through multiple environments, each of which poses a different sets of risks directly related to the effects of man-made climate change.
Take, for example, the Red Knot.
Red Knots belong to the large Sandpiper family of shorebirds. For most of the year, Red Knots feast on the small mollusks, crustaceans, and marine worms it finds by probing beneath the sand or mud with its beak. When nesting, it turns to insects (mostly flies and mosquitos) and (when insects prove scarce) vegetation, including plant seeds, shoots, buds, and leaves.
Of the six Red Knot subspecies, two undertake grueling annual migrations of 19,000 miles and 15,000 miles, respectively. And climate change negatively effects both species along their routes, threatening each with extinction in the decades ahead.
The Red Knot with the “shorter” migration route hails from Africa. Calidris canutus canutus—“canutus,” for short) flies from as far south as South Africa to Mauritania in West Africa and at various stopovers in Eastern Europe and the Netherlands before reaching it breeding territory in the Russian Arctic.
For the canutus Red Knot, climate change has disrupted the well-synchronized timing of its migration. Warming caused by climate change affects polar regions far more than it effects the climate zones in between them, and in the Arctic snow has been melting earlier each year. “Analysis of satellite images have shown that over the past 33 years, snow at the Red Knot’s breeding grounds has progressively melted earlier, at a rate of half a day per year, so that’s now more than two weeks,” according to Jan van Gils of the Royal Netherlands Institute for Sea Research.
The problem? Timing. For centuries, Red Knot have begun nesting on the Arctic tundra while snow remained on the ground. Three weeks later, when the chicks hatched, a bonanza of flying insects awaited both parents and chicks. No longer. When the Red Knot arrive now, the insect population is already at or beyond peak. By the time the chicks hatch, less prey remains available to them, and ornithologists studying the canutus Red Knot have noticed that young birds return to wintering grounds smaller in size than previous generations and with shorter beaks. The smaller size makes it hard for them to keep up and compete with larger birds; and the shorter beaks make it harder for them to reach the energy-rich mollusks, crustaceans, and marine worms they’d normally eat as they fly south and at their wintering areas. Instead they turn to a less nutritious food source: sea grass. “This new diet,” notes Carl Zimmer of the New York Times, “appears to be taking a toll: Dr. van Gils and his colleagues have found that juvenile red knots with short bills are more likely to die than birds with long bills.”
As disturbing as this trend may be, the plight of the American species of Red Knot (Calidris canutus rufa) is even more dire. The rufa Red Knot annually files from as far south as the Tierra del Fuego, the southern tip of South America, to Arctic breeding grounds in the Hudson Bay region. It accomplishes this incredible journey by flying thousands of miles at a time, temporarily interrupting its migration north with stopovers in Brazil and the mid-Atlantic coast of the U.S. for rest and much needed food.
Thirty years ago, as many as 150,000 rufa Red Knot made the annual polar migration to and from the Canadian Arctic. But a variety of man-made factors have caused the population of rufa Red Knot to plummet to below 20,000 birds:
Habitat Loss. Development (in Florida and up the Mid-Atlantic coast) have encroached on territory Red Knot have long depended on for rest and food. Seawalls, jetties, and similar structures have increased beach erosion. And rising waters (caused by climate change) have inundated barrier islands and reduced the breadth of tidal flats foraged by migrating shorebirds.
Overfishing. Nearly 30 years of over-harvesting has reduced the population of Horseshoe Crab in the Delaware Bay, and the remaining crabs have found less suitable habitat when emerging from the sea to breed. Red Knot and other shorebird species gorge on the eggs that Horseshoe Crab lay on Delaware beaches, and the diminished quantity of available eggs has taken a significant toll on the rufa Red Knot.
Global Warming. The direct result of climate change, warming has increased sea levels (flooding barrier islands and reducing shoreline). It has also increased the number of winter storms and the severity of storm surge, resulting in even further beach and shoreline erosion. The increased temperature of sea water has also forced clams and molluscs to abandon historic mid-Atlantic territories and migrate further north along the Atlantic coastline, forcing Red Knot and other shorebirds to fly even further to find energy-rich food for their arduous journey.
“As their world heats up,” Deborah Cramer explains in “Red Knots Are Battling Climate Change—On Both Ends of the Earth,” the rufa Red Knots
“are threatened almost everywhere along their flyway: The warming, acidic sea inhibits the growth of the shellfish the birds need to fuel their impressive migration; rising seas may flood their seaside homes; rising temperatures threaten to shrink their Arctic nesting grounds and expose them to more predators. No matter where they go, no matter how many new homes they might seek, Red Knots can’t escape the effects of global warming.”
On January 12, 2015, in response to the shorebird’s declining numbers, the U.S. Fish and Wildlife Service afforded Calidris canutus rufa Threatened Species Status under the Endangered Species Act.
A sentinel species, it is the first bird species listed as Threatened or Endangered specifically due to climate change. Unfortunately, it is almost surely the first of many more to come.
To learn more about the plight of such migrating shorebirds as the Red Knot, consider the following sources:
Rufa Red Knot Articles:
• Red Knots Are Battling Climate Change—On Both Ends of the Earth
• The Bird that Travels 29,000km a Year
• In the Red: Climate Change Threatens Red Knot Population
• Red Knot [U.S. Fish and Wildlife Service]
• ECOS Environmental Conservation Online System: Red Knot
• U.S. Fish and Wildlife Rufa Listing
Canutus Red Knot Articles:
• Climate Change Shrinking Red Knots, Decreasing Survival Rates Of Smaller Birds
• Climate Change and the Case of the Shrinking Red Knots
• Climate Change Not Good For Red Knots
• Climate change is causing this bird to shrink: Study
• Size Of Migratory Bird Red Knot Shrinking Due To Climate Change